1. Field of the Invention
This invention relates to tunnel boring machines. In one embodiment, the invention relates to a full-face rotary cutterhead, double shield tunnel boring machine that is adapted to bore through a variety of geological structures, ranging from self-supporting rock to that requiring continuous lining support. The disclosed machine has high thrust capability for hard rock applications and a double shield to support poor ground until tunnel supports can be installed. A novel feature of the present invention, which is not limited to double shield machines, is that the primary propel cylinders are arranged in a series of at least three pairs in staggered pattern to perform the multiple functions of providing forward thrust, transmission of reaction torque, steering control, and roll corrections. Each propel cylinder is individually controllable and the propel cylinder pairs can be operated in either the forward thrust mode or in a hold-back mode for steering and roll corrections. This hold-back feature provides positive steering for the front portion of the machine.
2. Description of the Prior Art
The prior art includes the double shield tunnel boring machine disclosed in Robbins et al U.S. Pat. No. 4,420,188. The novel improvement in the present invention over that shown in the Robbins et al patent involves the use of a series of at least three pairs of hydraulic primary propel cylinders between the first and second shields, with each pair of primary propel cylinders being arranged in a V-shaped configuration having an included angle of about 15.degree. to 60.degree. in a plane generally parallel to the adjacent portions of the shields and with the line bisecting the included angle being substantially parallel to the longitudinal centerline of the machine. The pairs of primary propel cylinders rigidly tie the first and second shields together and perform the multiple functions of axial thrust (by simultaneous actuation), of transmitting reaction torque from the cutterhead support to the gripper system thereby countering the reverse rotary displacement of the cutterrhead support caused by the rotary torque applied to the cutterhead, of steering (by selective actuation causing angular displacement of the first shield, the cutterhead support, and the cutterhead relative to the second shield which is held stationary by the gripper system), and of roll correction (by selective actuation causing clockwise or counterclockwise rotation of the first shield, the cutterhead support, and the cutterhead relative to the second shield which is held stationary by the gripper system). Thus, the novel primary propel cylinder pairs have a forward thrust function, a reaction torque function, a steering function, and a roll correction function. They provide at all times a rigid structure between the first and second shields, replacing the conventional axially disposed rearwardly extendable thrust cylinders (such as the thrust rams 52 in Robbins et al U.S. Pat. No. 4,420,188), eliminating the need for separate reaction torque cylinders (such as the reaction torque cylinders 152 and 154 in the Robbins et al. patent), and also eliminating the need for precise control of the length of the reaction torque cylinders during the axial thrust stroke (such as in the Robbins et al patent where, in order to maintain the first shield nonrotative with respect to the second shield, the extension of the torque cylinders 152 and 154 had to progressively change during the pivotal movement thereof caused by the forward axial movement of the first shield).